1. Field of the Invention
The present invention relates to voice gateways for setting up a call via an IP (Internet Protocol) network, and more particularly to a route selection method of the voice gateways for determining a destination for setting up the call.
2. Description of the Related Art
Conventionally, a call system via the IP network or the like can reduce communication costs by effectively making use of network bands. For this reason, a demand for utilizing long distance calls and the like of the call system via the IP network is high.
FIG. 1 illustrates an example of a conventional route selection method.
In this diagram, a telephone switching network 10 and an IP network 12 are connected via voice gateways 201 to 20n, each having an office number indicating a location in the telephone switching network 10 and a transport address indicating a location in the IP network 12. Telephone terminals 501 to 50p connected to the telephone switching network 10 or telephone terminals 401 to 40n respectively connected to the voice gateways 201 to 20n can communicate with each other via the telephone switching network 10 or the IP network 12. An address determination server 30 will be described later.
In a case where the telephone terminal 401 calls the telephone terminal 40m via the IP network 12, the telephone terminal 401 sends to the voice gateway 201 a telephone number of the telephone terminal 40m as a destination, and the voice gateway 201 then determines a transport address after receiving the telephone number of the telephone terminal 40m. The transport address indicates a location of the voice gateway 20n as a destination for setting up the call in the IP network 12. Thus, the voice gateway 201 sends out a call-setup signal towards the transport address, and if the call is set up, then a communication (talk) is started between the telephone terminal 401 and the telephone terminal 40m.
Conventionally, there are two methods for the voice gateway 201 to determine the transport address of the destination voice gateway 20n for setting up the call according to the telephone number of the destination telephone terminal 40m.
In the first method, the voice gateways 201 to 20n each hold a table in which are recorded office numbers and corresponding transport addresses of all of the voice gateways 201 to 20n existing in the IP network 12. In the call setup, the transport address of the destination voice gateway is determined by referring to the table.
In the second method, the IP network is provided with the address determination server 30 having the table described in the first method. In the call setup, the transport address of the destination voice gateway is determined by inquiring of the address determination server 30.
However, the above-described two methods have the following disadvantages.
With respect to the first method, each voice gateway has the table in which are recorded the office numbers and the corresponding transport addresses of all of the voice gateways 201 to 20n existing in the IP network 12. For this reason, when an office number or a transport address of one voice gateway is changed due to the voice gateway being moved, the tables of all the other voice gateways must be changed. This brings about a problem of maintenance management.
With respect to the second method, whenever a call is generated, traffic is generated between the respective voice gateways 201 to 20n and the address determination server 30. For this reason, a load on the address determination server 30 is too heavy. That is, inquiries from a plurality of the voice gateways are concentrated on the one address determination server 30. This brings about the address determination server 30 operating late or congestion occurring at a point of connecting the address determination server 30 and the IP network 12. Moreover, even if a plurality of such address determination servers are disposed to disperse the traffic, as a result, costs go up and the problems of the above-described first method occur.